Apparatus and method for removing breathing motion artifacts in ct scans

ABSTRACT

A method and apparatus for removing breathing motion artifacts in imaging CT scans is disclosed. The method acquires raw imaging data from a CT scanner, and processes the raw CT imaging data by removing motion-induced artifacts via a motion model. Processing the imaging data may be achieved by initially estimating a 3D image to provide an estimate of raw sinogram image data, comparing the estimate to an actual CT sinogram, determining a difference between the sinograms, and iteratively reconstructing the 3D image by using the difference to alter the 3D image until the sinograms agree, wherein the 3D image moves according to the motion model.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and is a 35 U.S.C. § 111(a)continuation of, PCT international application number PCT/US2019/023706filed on Mar. 22, 2019, incorporated herein by reference in itsentirety, which claims priority to, and the benefit of, U.S. provisionalpatent application Ser. No. 62/646,968 filed on Mar. 23, 2018,incorporated herein by reference in its entirety. Priority is claimed toeach of the foregoing applications.

The above-referenced PCT international application was published as PCTInternational Publication No. WO 2019/183562 A1 on Sep. 26, 2019, whichpublication is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

A portion of the material in this patent document may be subject tocopyright protection under the copyright laws of the United States andof other countries. The owner of the copyright rights has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the United States Patent andTrademark Office publicly available file or records, but otherwisereserves all copyright rights whatsoever. The copyright owner does nothereby waive any of its rights to have this patent document maintainedin secrecy, including without limitation its rights pursuant to 37C.F.R. § 1.14.

BACKGROUND 1. Technical Field

The technology of this disclosure pertains generally to medical imaging,and more particularly to medical imaging during patient motion.

2. Background Discussion

Accurate biomechanical modeling relies on accurate tissue deformationmeasurements, which themselves require artifact-free images.Patient-induced image motion blurring impacts all breathing CT scans ofthe thorax and upper abdomen. For radiation therapy, this degrades imagequality and image registration accuracy. For pulmonology and upperabdomen imaging, this degrades the ability to use the scan for diagnosisor treatment response monitoring.

In pulmonology and upper abdominal imaging, the existing state of theart is to make Computed Tomography (CT) scanners faster, but they havereached their practical limit. With modern CT scanners, fast helicalfree breathing CT scans can be conducted extremely quickly and the timeimaging any one location in the patient is less than 0.3 s. While thisshort amount of time reduces motion-induced image artifacts, it does noteliminate the artifacts. In cardiac imaging, motion modeling isgenerally integrated into the image reconstruction process. While,cardiac imaging may take advantage of the regularity of the cardiaccycle, the breathing cycle can be very irregular, so these techniques donot work when removing motion artifacts from lung or upper abdomenimaging.

Accordingly, modern CT-based pulmonology research relies on breath-holdCT, i.e. where the patient is asked to hold their breath. However, thereare some circumstances when this is neither possible nor desired. Somepatients are unable to hold their breath, whether due to lung disease orinability to understand or follow breath hold instructions.

There are also some imaging studies that are intended to measure orevaluate the patient under free breathing or other conditions, soholding their breath is undesirable, as breath-hold CT removes oreliminates any ability to measure dynamically relevant features ofbreathing.

There are no existing methods for reducing motion blurring except breathhold. This is impractical for some patients and limits the diagnosticinformation for pulmonology and upper abdominal imaging applications.

BRIEF SUMMARY

One aspect of the present disclosure is a method and apparatus forremoving breathing motion artifacts in imaging CT scans by, for example,(i) acquiring raw imaging data from a CT scanner as an input; (ii)processing the raw CT imaging data by removing motion-induced artifacts;and (iii) outputting an artifact-free image; (iv) wherein processing theraw CT imaging data comprises initially estimating a 3D image to providean estimate of raw sinogram image data, comparing the estimate to anactual CT sinogram, determining a difference between the sinograms, anditeratively reconstructing the 3D image by using the difference to alterthe 3D image until the sinograms agree; and (v) wherein the 3D imagemoves according to a predetermined motion model.

The systems and methods of the present technology use an iterativeprocess to produce a CT scan image of a free-breathing patient with thespatial resolution as though the patient had held their breath.

While the systems and methods disclosed herein are depicted and detailedwith respect to removing breathing motion artifacts for CT imaging, itis appreciated that the systems and methods may be used for removing anymotion artifact (e.g. from other patient musculature) in any number ofimaging modalities (e.g. MRI, ultrasound, etc.)

Further aspects of the technology described herein will be brought outin the following portions of the specification, wherein the detaileddescription is for the purpose of fully disclosing preferred embodimentsof the technology without placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The technology described herein will be more fully understood byreference to the following drawings which are for illustrative purposesonly:

FIG. 1 shows a schematic process flow diagram of a first embodiment ofthe presented technology in which the target anatomy of the 3D image tobe reconstructed is not static and moves during the time of the imagingscan acquisition.

FIG. 2 shows a schematic process flow diagram of a second embodiment ofthe presented technology in which the reconstructed 3D image is notstatic and moves according to a motion model determined as part of theiterative reconstruction process.

FIG. 3 shows a schematic system diagram for removing motion artifactsusing the methods of the presented technology.

DETAILED DESCRIPTION

Modern CT scanners acquire images very quickly, moving the patient asthe CT scanner rotates. This is termed helical scanning and is used formost CT scanning image acquisition. Breathing motion induces artifactsand blurring in the images that can degrade the diagnostic utility ofthe images. Under breathing conditions, standard helical CTreconstruction yields artifacts. In contrast to traditional iterativeapproaches, the 3D image in the methods disclosed herein is not staticduring the time represented by the CT scan acquisition.

FIG. 1 shows a schematic process flow diagram of a first imaging method10 for 3D imaging of non-static target subject matter to create a static3D image without breathing motion artifacts. CT projections (sinograms)12 are acquired from the CT scanner as a series of frames. Method 10employs a motion model estimation 14 along with the CT projection 12(the raw sinogram data used by CT scanners to reconstruct the image) tothe image reconstruction process. In this method, the generated 3D imagewill move according to the predetermined breathing motion model 14. In apreferred embodiment, the motion estimation model uses a reference image16. The reference image 16 may comprise a 3D image that can be apreviously acquired CT scan, a CT scan reconstructed from a previousiteration, or other source of 3D image. The reference image 16 isrepresentative of the patient's tissue geometry at a specific breathingphase, for example at exhalation. An iterative reconstruction 20 is thenemployed with the motion model 14 to generate a CT scan 22 withoutmotion artifacts.

FIG. 2 shows a method 30, the motion model 14 is determined as part ofthe iterative reconstruction step 20 with the acquired sinograms 12 togenerate a CT scan 22 without motion artifacts. In method 30, theiterative reconstruction step 20 creates both an image without breathingmotion artifacts 22 and simultaneously a breathing motion model 14. Boththe model 14 and the image 22 are iterated such that a final qualitymetric, such as image sharpness, is optimized. As the motion model 14 isimproved, the iterated images will get sharper and sharper, withreductions in motion artifacts, until no more improvement can be made.At that point, the breathing motion used in the iteration will be thebreathing motion model 14.

FIG. 3, shows schematic diagram of a system 50 for removing motionartifacts using either of the methods of FIG. 1 or FIG. 2. System 50acquires the CT projections (series of sinogram frames) 12 of thesubject (e.g. patient) 56 via CT scanner 52. The acquired sinograms 12are used to reconstruct the 3D image of the target anatomy 56.

In one embodiment, one or more breathing motion surrogates 54 are input.Alternatively, the motion breathing model 14 may be generated from theimage data itself, e.g. the standard (original) CT images 58 or datarelating to time, CT gantry angle, etc. The breathing surrogate 54 maybe simultaneously integrated along with the raw sinogram data 12 and thebreathing motion model 14 to create motion artifact-reduced oreliminated images. The one or more breathing surrogates 54 may comprisean image from an external noninvasive system such as a spirometer orabdominal belt, camera-based system, or the like.

A computer 60 may be used to process the acquired CT and reference dataaccording to application programming 64, which may comprise instructionsthat are stored in memory 66 and executable on processor 62 to employthe methods 10/30 for generated the motion-artifact removal describedherein.

In a preferred embodiment, the motion model estimation 14 and imagereconstruction 20 processes are conducted in an interleaved fashion,typically alternating between the two until an adequate image quality isreached.

In one embodiment, application programming 64 is configured such thatthe motion model 14 is generated earlier or in a previous processiteration and coupled to the breathing motion surrogate 54, whichgenerally comprises a measured quantity that is quantitatively connectedto the breathing phase, for example spirometry-measured tidal volume. Inanother embodiment, the motion model 14 is related to time or CT gantryangle.

Application programming 64 may employ a conventional iterativereconstruction method that applies the motion model 14 to the iteratedimage using motion that is consistent with the sinogram acquisition timeand subsequent surrogate value when appropriate. Examples of suitableiterative reconstruction methods include, but are limited to, the SARTmethod (see, for example, Andersen and Kak, “Simultaneous algebraicreconstruction technique (SART): A superior implementation of the ARTalgorithm”, Ultrasonic Imaging, 6, 81-94 (1984)) incorporated herein byreference. For CT reconstruction, the image is reconstructed such thatin each iteration, projections are cast through the current imageiteration, compared against the measured sinogram data, and theirdifferences cast back projected through the image to act as improvementsto the reconstructed image.

In one embodiment, the method 10 employs a breathing motion model thatis iteratively developed or updated by the motion estimation process. Areference image 16 is employed that is previously acquired or the outputof a previous image-reconstruction iteration. The motion model 14 isupdated using the CT sinogram data 12, typically one sinogram frame at atime. The reference image 16 is deformed using a vector field 18 that iscomputed using the motion model consistent with the time the sinogramframe was acquired (see FIG. 1). This vector field 18 is called theprevious model iteration generated vector field. Image projections arecalculated through the deformed image to the detector plane, forming acalculated sinogram frame. The calculated sinogram frame may be comparedagainst the measured sinogram frame using rigid or deformable imageregistration. The registration vectors, termed error vectors, are backprojected through the patient geometry. The projected error vectors areadded to the previous model iteration generated vector field. Thesevectors are in turn used to regenerate the next iteration of the motionmodel. The process is repeated at the next sinogram frame, where theorder of the analyzed sinogram frames may be in order of acquisitiontime, breathing surrogate value, or other order. The motion modelestimation process 14 is finalized when the calculated sinogram framesare sufficiently similar to the measured sinogram frames according to apredetermined criterion.

The motion model 14 may be published or unpublished and is means forconnecting the sinogram data to each other via a surrogate, time, or CTgantry angle, in such a way as to allow an image to be formed that hasgreatly reduced or no breathing motion artifacts.

The motion model 14 may be taken as a prior (defined earlier),iteratively generated in the image process, or taken as a prior andmodified in the image generation process. The motion model 14 can alsobe an output of the image generation process.

Rather than conducting traditional back projection, the systems andmethods of the present technology employ iterative reconstruction. Inone embodiment, an initial estimate of the 3D image is used andprojected through to provide an estimate of the raw sinogram image data.That estimate is then compared against the actual CT sinogram todetermine a difference, and the difference is then used to alter the 3Dimage until the sinograms agree.

Each of the foregoing embodiments utilizes an iterative process toproduce a CT scan image of a free-breathing patient with the spatialresolution as though the patient had held their breath.

Embodiments of the present technology may be described herein withreference to flowchart illustrations of methods and systems according toembodiments of the technology, and/or procedures, algorithms, steps,operations, formulae, or other computational depictions, which may alsobe implemented as computer program products. In this regard, each blockor step of a flowchart, and combinations of blocks (and/or steps) in aflowchart, as well as any procedure, algorithm, step, operation,formula, or computational depiction can be implemented by various means,such as hardware, firmware, and/or software including one or morecomputer program instructions embodied in computer-readable programcode. As will be appreciated, any such computer program instructions maybe executed by one or more computer processors, including withoutlimitation a general-purpose computer or special purpose computer, orother programmable processing apparatus to produce a machine, such thatthe computer program instructions which execute on the computerprocessor(s) or other programmable processing apparatus create means forimplementing the function(s) specified.

Accordingly, blocks of the flowcharts, and procedures, algorithms,steps, operations, formulae, or computational depictions describedherein support combinations of means for performing the specifiedfunction(s), combinations of steps for performing the specifiedfunction(s), and computer program instructions, such as embodied incomputer-readable program code logic means, for performing the specifiedfunction(s). It will also be understood that each block of the flowchartillustrations, as well as any procedures, algorithms, steps, operations,formulae, or computational depictions and combinations thereof describedherein, can be implemented by special purpose hardware-based computersystems which perform the specified function(s) or step(s), orcombinations of special purpose hardware and computer-readable programcode.

Furthermore, these computer program instructions, such as embodied incomputer-readable program code, may also be stored in one or morecomputer-readable memory or memory devices that can direct a computerprocessor or other programmable processing apparatus to function in aparticular manner, such that the instructions stored in thecomputer-readable memory or memory devices produce an article ofmanufacture including instruction means which implement the functionspecified in the block(s) of the flowchart(s). The computer programinstructions may also be executed by a computer processor or otherprogrammable processing apparatus to cause a series of operational stepsto be performed on the computer processor or other programmableprocessing apparatus to produce a computer-implemented process such thatthe instructions which execute on the computer processor or otherprogrammable processing apparatus provide steps for implementing thefunctions specified in the block(s) of the flowchart(s), procedure (s)algorithm(s), step(s), operation(s), form ula (e), or computationaldepiction(s).

It will further be appreciated that the terms “programming” or “programexecutable” as used herein refer to one or more instructions that can beexecuted by one or more computer processors to perform one or morefunctions as described herein. The instructions can be embodied insoftware, in firmware, or in a combination of software and firmware. Theinstructions can be stored local to the device in non-transitory mediaor can be stored remotely such as on a server, or all or a portion ofthe instructions can be stored locally and remotely. Instructions storedremotely can be downloaded (pushed) to the device by user initiation, orautomatically based on one or more factors.

It will further be appreciated that as used herein, that the termsprocessor, hardware processor, computer processor, central processingunit (CPU), and computer are used synonymously to denote a devicecapable of executing the instructions and communicating withinput/output interfaces and/or peripheral devices, and that the termsprocessor, hardware processor, computer processor, CPU, and computer areintended to encompass single or multiple devices, single core andmulticore devices, and variations thereof.

From the description herein, it will be appreciated that the presentdisclosure encompasses multiple embodiments which include, but are notlimited to, the following:

1. An apparatus for removing motion-induced artifacts in a scannedimage, the apparatus comprising: (a) a computer processor; and (b) anon-transitory computer-readable memory storing instructions executableby the computer processor; (c) wherein said instructions, when executedby the computer processor, perform steps comprising: (i) acquiring rawimaging data of a moving target anatomy from an image scanner; (ii)generating a reference image representative of the target anatomygeometry at a specific phase of motion; (iii) generating a motion modelas a function of the reference image; (iv) iteratively reconstructing a3D image of the target anatomy with the motion model to removemotion-induced artifacts from the image; and (v) outputting a motionartifact-free 3D image.

2. The apparatus or method of any preceding or subsequent embodiment,wherein the 3D image moves according to the motion model.

3. The apparatus or method of any preceding or subsequent embodiment,wherein the motion-induced artifacts comprise breathing motion of thetarget anatomy, and wherein the image is representative of the targetanatomy at a specific breathing phase.

4. The apparatus or method of any preceding or subsequent embodiment,wherein the raw imaging data comprises a computed tomography (CT)sinograms acquired as a series of frames.

5. The apparatus or method of any preceding or subsequent embodiment,wherein the reference image of the target anatomy is generated from oneor more of: a previously acquired imaging scan or sinogram, an imagingscan reconstructed from a previous scan iteration, or a 3D imageacquired from another source.

6. The apparatus or method of any preceding or subsequent embodiment:(vi) wherein generating a reference image comprises estimating areference 3D image to provide an estimate of the acquired sinogram imagedata; and (vii) wherein iteratively reconstructing a 3D image comprisescomparing the estimate to an acquired sinogram and determining adifference between the reference 3D image and the acquired sinogram, anditeratively reconstructing the 3D image by using the determineddifference to alter the 3D image until the reference 3D image and theacquired sinogram agree.

7. The apparatus or method of any preceding or subsequent embodiment,wherein the motion model is generated via a breathing motion surrogatethat is quantitatively coupled to the breathing phase.

8. The apparatus or method of any preceding or subsequent embodiment,wherein the breathing motion surrogate is a function of one or more ofspirometry-measured tidal volume or CT gantry angle.

9. The apparatus or method of any preceding or subsequent embodiment,wherein the breathing motion surrogate comprises an image acquired froman external noninvasive device.

10. The apparatus or method of any preceding or subsequent embodiment,wherein the 3D image is reconstructed such that in each iteration, oneor more projections are cast through a current image iteration andcompared against measured sinogram data, wherein differences between thecurrent image iteration and measured sinogram data are castback-projected through the 3D image to improve the 3D image.

11. A system for removing breathing motion artifacts in CT scans, thesystem comprising: (a) a CT scanner; (b) a computer processor; and (c) anon-transitory computer-readable memory storing instructions executableby the computer processor; (d) wherein said instructions, when executedby the computer processor, perform steps comprising: (i) acquiring rawimaging data of a moving target anatomy from the CT scanner, the rawimaging data comprising sinograms acquired as a series of frames; (ii)generating a reference image representative of the target anatomygeometry at a specific phase of motion; (iii) generating a motion modelas a function of the reference image; (iv) iteratively reconstructing a3D image of the target anatomy with the motion model to removemotion-induced artifacts from the image; and (v) outputting a motionartifact-free 3D image.

12. The apparatus or method of any preceding or subsequent embodiment,wherein the 3D image moves according to the motion model.

13. The apparatus or method of any preceding or subsequent embodiment,wherein the motion-induced artifacts comprise breathing motion of thetarget anatomy, and wherein the image is representative of the targetanatomy at a specific breathing phase.

14. The apparatus or method of any preceding or subsequent embodiment,wherein the reference image of the target anatomy is generated from oneor more of: a previously acquired imaging scan or sinogram, an imagingscan reconstructed from a previous scan iteration, or a 3D imageacquired from another source.

15. The apparatus or method of any preceding or subsequent embodiment:(vi) wherein generating a reference image comprises estimating areference 3D image to provide an estimate of the acquired sinogram imagedata; and (vii) wherein iteratively reconstructing a 3D image comprisescomparing the estimate to an acquired sinogram and determining adifference between the reference 3D image and the acquired sinogram, anditeratively reconstructing the 3D image by using the determineddifference to alter the 3D image until the reference 3D image and theacquired sinogram agree.

16. The apparatus or method of any preceding or subsequent embodiment,wherein the motion model is generated via a breathing motion surrogatethat is quantitatively coupled to the breathing phase.

17. The apparatus or method of any preceding or subsequent embodiment,wherein the breathing motion surrogate is a function of one or more ofspirometry-measured tidal volume or CT gantry angle.

18. The apparatus or method of any preceding or subsequent embodiment,wherein the breathing motion surrogate comprises an image acquired froman external noninvasive device.

19. The apparatus or method of any preceding or subsequent embodiment,wherein the 3D image is reconstructed such that in each iteration, oneor more projections are cast through a current image iteration andcompared against measured sinogram data, wherein differences between thecurrent image iteration and measured sinogram data are castback-projected through the 3D image to improve the 3D image.

20. A computer implemented method for removing motion-induced artifactsin a scanned image, the method comprising: (a) acquiring raw imagingdata of a moving target anatomy from an image scanner; (b) generating areference image representative of the target anatomy geometry at aspecific phase of motion; (c) generating a motion model as a function ofthe reference image; (d) iteratively reconstructing a 3D image of thetarget anatomy with the motion model to remove motion-induced artifactsfrom the image; and (e) outputting a motion artifact-free 3D image; (f)wherein said method is performed by a computer processor executinginstructions stored on a non-transitory computer-readable medium.

21. The apparatus or method of any preceding or subsequent embodiment,wherein the 3D image moves according to the motion model.

22. The apparatus or method of any preceding or subsequent embodiment,wherein the motion-induced artifacts comprise breathing motion of thetarget anatomy, and wherein the image is representative of the targetanatomy at a specific breathing phase.

23. The apparatus or method of any preceding or subsequent embodiment,wherein the raw imaging data comprises a computed tomography (CT)sinograms acquired as a series of frames.

24. The apparatus or method of any preceding or subsequent embodiment,wherein the reference image of the target anatomy is generated from oneor more of: a previously acquired imaging scan or sinogram, an imagingscan reconstructed from a previous scan iteration, or a 3D imageacquired from another source.

25. The apparatus or method of any preceding or subsequent embodiment:(g) wherein generating a reference image comprises estimating areference 3D image to provide an estimate of the acquired sinogram imagedata; and (h) wherein iteratively reconstructing a 3D image comprisescomparing the estimate to an acquired sinogram and determining adifference between the reference 3D image and the acquired sinogram, anditeratively reconstructing the 3D image by using the determineddifference to alter the 3D image until the reference 3D image and theacquired sinogram agree.

26. The apparatus or method of any preceding or subsequent embodiment,wherein the motion model is generated via a breathing motion surrogatethat is quantitatively coupled to the breathing phase.

27. The apparatus or method of any preceding or subsequent embodiment,wherein the breathing motion surrogate is a function of one or more ofspirometry-measured tidal volume or CT gantry angle.

28. The apparatus or method of any preceding or subsequent embodiment,wherein the breathing motion surrogate comprises an image acquired froman external noninvasive device.

29. The apparatus or method of any preceding or subsequent embodiment,wherein the 3D image is reconstructed such that in each iteration, oneor more projections are cast through a current image iteration andcompared against measured sinogram data, wherein differences between thecurrent image iteration and measured sinogram data are castback-projected through the 3D image to improve the 3D image.

As used herein, the singular terms “a,” “an,” and “the” may includeplural referents unless the context clearly dictates otherwise.Reference to an object in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”

As used herein, the term “set” refers to a collection of one or moreobjects. Thus, for example, a set of objects can include a single objector multiple objects.

As used herein, the terms “substantially” and “about” are used todescribe and account for small variations. When used in conjunction withan event or circumstance, the terms can refer to instances in which theevent or circumstance occurs precisely as well as instances in which theevent or circumstance occurs to a close approximation. When used inconjunction with a numerical value, the terms can refer to a range ofvariation of less than or equal to ±10% of that numerical value, such asless than or equal to ±5%, less than or equal to ±4%, less than or equalto ±3%, less than or equal to ±2%, less than or equal to ±1%, less thanor equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to±0.05%. For example, “substantially” aligned can refer to a range ofangular variation of less than or equal to ±10°, such as less than orequal to ±5°, less than or equal to ±4°, less than or equal to ±3°, lessthan or equal to ±2°, less than or equal to ±1°, less than or equal to±0.5°, less than or equal to ±0.1°, or less than or equal to ±0.05°.

Additionally, amounts, ratios, and other numerical values may sometimesbe presented herein in a range format. It is to be understood that suchrange format is used for convenience and brevity and should beunderstood flexibly to include numerical values explicitly specified aslimits of a range, but also to include all individual numerical valuesor sub-ranges encompassed within that range as if each numerical valueand sub-range is explicitly specified. For example, a ratio in the rangeof about 1 to about 200 should be understood to include the explicitlyrecited limits of about 1 and about 200, but also to include individualratios such as about 2, about 3, and about 4, and sub-ranges such asabout 10 to about 50, about 20 to about 100, and so forth.

Although the description herein contains many details, these should notbe construed as limiting the scope of the disclosure but as merelyproviding illustrations of some of the presently preferred embodiments.Therefore, it will be appreciated that the scope of the disclosure fullyencompasses other embodiments which may become obvious to those skilledin the art.

All structural and functional equivalents to the elements of thedisclosed embodiments that are known to those of ordinary skill in theart are expressly incorporated herein by reference and are intended tobe encompassed by the present claims. Furthermore, no element,component, or method step in the present disclosure is intended to bededicated to the public regardless of whether the element, component, ormethod step is explicitly recited in the claims. No claim element hereinis to be construed as a “means plus function” element unless the elementis expressly recited using the phrase “means for”. No claim elementherein is to be construed as a “step plus function” element unless theelement is expressly recited using the phrase “step for”.

What is claimed is:
 1. An apparatus for removing motion-inducedartifacts in a scanned image, the apparatus comprising: (a) a computerprocessor; and (b) a non-transitory computer-readable memory storinginstructions executable by the computer processor; (c) wherein saidinstructions, when executed by the computer processor, perform stepscomprising: (i) acquiring raw imaging data of a moving target anatomyfrom an image scanner; (ii) generating a reference image representativeof the target anatomy geometry at a specific phase of motion; (iii)generating a motion model as a function of the reference image; (iv)iteratively reconstructing a 3D image of the target anatomy with themotion model to remove motion-induced artifacts from the image; and (v)outputting a motion artifact-free 3D image.
 2. The apparatus of claim 1,wherein the 3D image moves according to the motion model.
 3. Theapparatus of claim 1, wherein the motion-induced artifacts comprisebreathing motion of the target anatomy, and wherein the image isrepresentative of the target anatomy at a specific breathing phase. 4.The apparatus of claim 3, wherein the raw imaging data comprises acomputed tomography (CT) sinograms acquired as a series of frames. 5.The apparatus of claim 4, wherein the reference image of the targetanatomy is generated from one or more of: a previously acquired imagingscan or sinogram, an imaging scan reconstructed from a previous scaniteration, or a 3D image acquired from another source.
 6. The apparatusof claim 4: (vi) wherein generating a reference image comprisesestimating a reference 3D image to provide an estimate of the acquiredsinogram image data; and (vii) wherein iteratively reconstructing a 3Dimage comprises comparing the estimate to an acquired sinogram anddetermining a difference between the reference 3D image and the acquiredsinogram, and iteratively reconstructing the 3D image by using thedetermined difference to alter the 3D image until the reference 3D imageand the acquired sinogram agree.
 7. The apparatus of claim 4, whereinthe motion model is generated via a breathing motion surrogate that isquantitatively coupled to the breathing phase.
 8. The apparatus of claim7, wherein the breathing motion surrogate is a function of one or moreof spirometry-measured tidal volume or CT gantry angle.
 9. The apparatusof claim 7, wherein the breathing motion surrogate comprises an imageacquired from an external noninvasive device.
 10. The apparatus of claim6, wherein the 3D image is reconstructed such that in each iteration,one or more projections are cast through a current image iteration andcompared against measured sinogram data, wherein differences between thecurrent image iteration and measured sinogram data are castback-projected through the 3D image to improve the 3D image.
 11. Asystem for removing breathing motion artifacts in CT scans, the systemcomprising: (a) a CT scanner; (b) a computer processor; and (c) anon-transitory computer-readable memory storing instructions executableby the computer processor; (d) wherein said instructions, when executedby the computer processor, perform steps comprising: (i) acquiring rawimaging data of a moving target anatomy from the CT scanner, the rawimaging data comprising sinograms acquired as a series of frames; (ii)generating a reference image representative of the target anatomygeometry at a specific phase of motion; (iii) generating a motion modelas a function of the reference image; (iv) iteratively reconstructing a3D image of the target anatomy with the motion model to removemotion-induced artifacts from the image; and (v) outputting a motionartifact-free 3D image.
 12. The system of claim 11, wherein the 3D imagemoves according to the motion model.
 13. The system of claim 11, whereinthe motion-induced artifacts comprise breathing motion of the targetanatomy, and wherein the image is representative of the target anatomyat a specific breathing phase.
 14. The system of claim 11, wherein thereference image of the target anatomy is generated from one or more of:a previously acquired imaging scan or sinogram, an imaging scanreconstructed from a previous scan iteration, or a 3D image acquiredfrom another source.
 15. The system of claim 13: (vi) wherein generatinga reference image comprises estimating a reference 3D image to providean estimate of the acquired sinogram image data; and (vii) whereiniteratively reconstructing a 3D image comprises comparing the estimateto an acquired sinogram and determining a difference between thereference 3D image and the acquired sinogram, and iterativelyreconstructing the 3D image by using the determined difference to alterthe 3D image until the reference 3D image and the acquired sinogramagree.
 16. The system of claim 13, wherein the motion model is generatedvia a breathing motion surrogate that is quantitatively coupled to thebreathing phase.
 17. The system of claim 16, wherein the breathingmotion surrogate is a function of one or more of spirometry-measuredtidal volume or CT gantry angle.
 18. The system of claim 16, wherein thebreathing motion surrogate comprises an image acquired from an externalnoninvasive device.
 19. The system of claim 15, wherein the 3D image isreconstructed such that in each iteration, one or more projections arecast through a current image iteration and compared against measuredsinogram data, wherein differences between the current image iterationand measured sinogram data are cast back-projected through the 3D imageto improve the 3D image.
 20. A computer implemented method for removingmotion-induced artifacts in a scanned image, the method comprising: (a)acquiring raw imaging data of a moving target anatomy from an imagescanner; (b) generating a reference image representative of the targetanatomy geometry at a specific phase of motion; (c) generating a motionmodel as a function of the reference image; (d) iterativelyreconstructing a 3D image of the target anatomy with the motion model toremove motion-induced artifacts from the image; and (e) outputting amotion artifact-free 3D image; (f) wherein said method is performed by acomputer processor executing instructions stored on a non-transitorycomputer-readable medium.
 21. The method of claim 20, wherein the 3Dimage moves according to the motion model.
 22. The method of claim 20,wherein the motion-induced artifacts comprise breathing motion of thetarget anatomy, and wherein the image is representative of the targetanatomy at a specific breathing phase.
 23. The method of claim 22,wherein the raw imaging data comprises a computed tomography (CT)sinograms acquired as a series of frames.
 24. The method of claim 23,wherein the reference image of the target anatomy is generated from oneor more of: a previously acquired imaging scan or sinogram, an imagingscan reconstructed from a previous scan iteration, or a 3D imageacquired from another source.
 25. The method of claim 20: (g) whereingenerating a reference image comprises estimating a reference 3D imageto provide an estimate of the acquired sinogram image data; and (h)wherein iteratively reconstructing a 3D image comprises comparing theestimate to an acquired sinogram and determining a difference betweenthe reference 3D image and the acquired sinogram, and iterativelyreconstructing the 3D image by using the determined difference to alterthe 3D image until the reference 3D image and the acquired sinogramagree.
 26. The method of claim 23, wherein the motion model is generatedvia a breathing motion surrogate that is quantitatively coupled to thebreathing phase.
 27. The method of claim 26, wherein the breathingmotion surrogate is a function of one or more of spirometry-measuredtidal volume or CT gantry angle.
 28. The method of claim 26, wherein thebreathing motion surrogate comprises an image acquired from an externalnoninvasive device.
 29. The method of claim 25, wherein the 3D image isreconstructed such that in each iteration, one or more projections arecast through a current image iteration and compared against measuredsinogram data, wherein differences between the current image iterationand measured sinogram data are cast back-projected through the 3D imageto improve the 3D image.